1. Field of the Invention
This invention relates to a linear light beam generating optical system for generating a linear light beam which is used in a system for rapidly heating or cooling a large area such as a laser annealing system.
2. Description of the Related Art
There have been known various technologies of linearly projecting a laser beam emitted from a semiconductor laser onto a surface and using the laser beam as a linear light beam. For example, such a linear light beam is used in the field of initialization of an optical disk or laser annealing.
In Japanese Unexamined Patent Publication No. 10(1998)-031820, there is disclosed an optical disk initialization system where a linear light beam projected onto a surface of a medium is used to initialize an optical disk. In the patent publication, there is a disclosure on an optical system which images a light beam emitted from a stripe-like broad area semiconductor laser on a disk as a linear image and various technologies of suppressing unevenness in a light intensity in a longitudinal light intensity distribution are disclosed.
In Japanese Unexamined Patent Publication No. 10(1998)-094892, there is disclosed a laser heating system which is employed, for instance, in a soldering system, and a method in which a laser beam emitted from a semiconductor laser is converged on the side of the slow axis and diverged on the side of the fast axis in order to convert a laser beam emitted from a broad area semiconductor laser into a linear light beam which has a longitudinally uniform intensity distribution is proposed. In the patent publication, a laser beam emitted from a semiconductor laser is projected onto a surface as a linear light beam extending in the direction of the fast axis.
Japanese Unexamined Patent Publication No. 5(1993)-021340 is on a technology of forming single-crystal semiconductor film on an insulating substrate and employs a laser beam as a heat source for zone melting recrystallization. In Japanese Unexamined Patent Publication No. 5(1993)-021340, a method where a beam spot collected on the target is scanned at high speed in a direction perpendicular to the scanning direction, thereby generating a pseudo linear light beam is disclosed as a specific method of realizing a linear light beam.
In an embodiment of Japanese Unexamined Patent Publication No. 2000-091231, there is disclosed a method of obtaining a linear light beam on a surface to be exposed to the light beam by arranging light beams emitted from a semiconductor laser array.
As described above, any of the technologies disclosed in Japanese Unexamined Patent Publication Nos. 10(1998)-031820, 10(1998)-094892, 5(1993)-021340 and 2000-091231 intends to obtain a linear light beam which is uniform in the intensity distribution in the longitudinal direction on a surface to be exposed.
However, since being for linearly shaping a laser beam emitted from a single semiconductor laser, any of the optical systems disclosed in Japanese Unexamined Patent Publication Nos. 10(1998)-031820, 10(1998)-094892, and 5(1993)-021340 has drawbacks that it cannot obtain a projecting light having a sufficient power and projection onto a large area is difficult especially at wavelengths, other than 810 nm and 980 nm, where it is difficult to obtain a high output power semiconductor laser.
Further, in accordance with the optical system disclosed in Japanese Unexamined Patent Publication No. 2000-091231, though a linear light beam covering a large area can be obtained by arranging a plurality of semiconductor lasers, the light beam cannot be sufficiently stopped in the direction of the fast axis since the intensity of the light beam is uniformed by the use of a homogenizer without taking into account the slow axis or the fast axis of the laser beam.